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The effect of a oxygen treatment on the electrochemical characteristics of a soft carbon anode material for Li-ion batteries was investigated. After a coke carbonization process at 1000 degrees C in an argon atmosphere, the samples were treated under a flow of oxygen gas to obtain a mild oxidation effect. After this oxygen treatment, the coke samples exhibited an improved initial coulombic efficiency and cycle performance as compared to the carbonized sample. High-resolution transmission electron microscopy revealed that the carbonized cokes consisted of disordered and nanosized graphene layers and the surface of the modified carbon was significantly changed after the treatment. The chemical state of the cokes was analyzed using X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The enhanced electrochemical properties of the surface modified cokes could be attributed to the mild oxidation effect induced by the oxygen treatment. The mild oxidation process could have led to the elimination of surface imperfections and the reinforcement of a solid electrolyte interphase film, which resulted in the improved electrochemical characteristics.

Two different types of granulated graphites were synthesized by blending and kneading of natural graphite with pitch followed by sintering methods. The electrochemical performances of granulated graphites were investigated as anode materials for use in Li-ion batteries. The blending type granulated graphite possesses a large amount of cavities and voids, while the kneading type granulated graphite has a relatively compact microstructure, which is responsible for a high tap density. Both granulated graphites show improved the initial coulombic efficiencies as a result of decrease of surface area by the granulations. In particular, the kneading type granulated graphite exhibits an excellent rate-capability without significant capacity loss. In addition, the thermal stabilities of both granulated graphites were also improved, which could be attributed to the decrease of active surface area due to pitch coating.

A potential solid electrolyte for realizing all‐solid‐state battery (ASB) technology has been discovered in the form of Li10GeP2S12 (LGPS), a lithium superionic conductor with a high ionic conductivity (≈12 mS cm−1). Unfortunately, the achievable Li+ conductivity of LGPS is limited in a sheet‐type composite electrode owing to the porosity of this electrode structure. For the practical implementation of LGPS, it is crucial to control the pore structures of the composite electrode, as well as the interfaces between the active materials and solid‐ electrolyte particles. Herein, the addition of an ionic liquid, N‐methyl‐N‐butylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([Py14][TFSI]), is proposed as a pore filler for constructing a highly reliable electrode structure using LGPS. [Py14][TFSI] is coated onto the surface of LGPS powder through a wet process and a sheet‐type composite electrode is prepared using a conventional casting procedure. The [Py14][TFSI]‐embedded composite electrode exhibits significantly improved reversible capacity and power characteristics. It is suggested that pore‐filling with [Py14][TFSI] is effective for increasing contact areas and building robust interfaces between the active materials and solid‐electrolyte particles, leading to the generation of additional Li+ pathways in the composite electrode of ASBs. [ABSTRACT FROM AUTHOR]

Nitrogen-doped carbon nanotubes (NCNTs) are directly grown on the surface of a three-dimensional (3D) Ni foam substrate by floating catalytic chemical vapor deposition (FCCVD). The electrochemical properties of the 3D NCNT-Ni foam are thoroughly examined as a potential electrode for non-aqueous redox flow batteries (RFBs). During synthesis, nitrogen atoms can be successfully doped onto the carbon nanotube (CNT) lattices by forming an abundance of nitrogen-based functional groups. The 3D NCNT-Ni foam electrode exhibits excellent electrochemical activities toward the redox reactions of [Fe (bpy) 3 ] 2+/3+ (in anolyte) and [Co(bpy) 3 ] +/2+ (in catholyte), which are mainly attributed to the hierarchical 3D structure of the NCNT-Ni foam electrode and the catalytic effect of nitrogen atoms doped onto the CNTs; this leads to faster mass transfer and charge transfer during operation. As a result, the RFB cell assembled with 3D NCNT-Ni foam electrodes exhibits a high energy efficiency of 80.4% in the first cycle; this performance is maintained up to the 50 th cycle without efficiency loss. [ABSTRACT FROM AUTHOR]

Although the exceptional theoretical specific capacity (1672 mAh g−1) of elemental sulfur makes lithium-sulfur (Li-S) batteries attractive for upcoming rechargeable battery applications (e.g., electrical vehicles, drones, unmanned aerial vehicles, etc.), insufficient cycle lives of Li-S cells leave a substantial gap before their wide penetration into commercial markets. Among the key features that affect the cyclability, the shuttling process involving polysulfides (PS) dissolution is most fatal. In an effort to suppress this chronic PS shuttling, herein, a separator coated with poled BaTiO3 or BTO particles is introduced. Permanent dipoles that are formed in the BTO particles upon the application of an electric field can effectively reject PS from passing through the separator via electrostatic repulsion, resulting in significantly improved cyclability, even when a simple mixture of elemental sulfur and conductive carbon is used as a sulfur cathode. The coating of BTO particles also considerably suppresses thermal shrinkage of the poly(ethylene) separator at high temperatures and thus enhances the safety of the cell adopting the given separator. The incorporation of poled particles can be universally applied to a wide range of rechargeable batteries (i.e., metal-air batteries) that suffer from cross-contamination of charged species between both electrodes. [ABSTRACT FROM AUTHOR]

Lithium-ion hybrid capacitors have attracted great interest due to their high specific energy relative to conventional electrical double-layer capacitors. Nevertheless, the safety issue still remains a drawback for lithium-ion capacitors in practical operational environments because of the use of metallic lithium. Herein, single-phase Li5FeO4 with an antifluorite structure that acts as an alternative lithium source (instead of metallic lithium) is employed and its potential use for lithium-ion capacitors is verified. Abundant Li+ amounts can be extracted from Li5FeO4 incorporated in the positive electrode and efficiently doped into the negative electrode during the first electrochemical charging. After the first Li+ extraction, Li+ does not return to the Li5FeO4 host structure and is steadily involved in the electrochemical reactions of the negative electrode during subsequent cycling. Various electrochemical and structural analyses support its superior characteristics for use as a promising lithium source. This versatile approach can yield a sufficient Li+-doping efficiency of >90 % and improved safety as a result of the removal of metallic lithium from the cell. [ABSTRACT FROM AUTHOR]

Abstract: The material stability of ramsdellite type Li2+x Ti3O7 has been investigated from the view of the correlation between structural and electrochemical behaviors during Li insertion and extraction. The interfacial reaction of Li2+x Ti3O7 is identified by using AC-impedance spectroscopy and various electrochemical measurements are carefully conducted to interpret each elemental reaction of the complicated interfacial reaction. The impedance spectra indicate three semi-circles in the frequency range from 1MHz to 5mHz which fit expectations well. Li+ insertion at the interface is explained by applying the adatom model that includes desolvation and absorption of lithium ions through electron transfer and lattice incorporation. [Copyright &y& Elsevier]

Abstract: Electrochemical behaviors of Sn and SnO anodes are studied. Charging/discharging curves show irreversible capacities at the first cycle in both Sn and SnO electrodes. The irreversible capacity loss in Sn electrode is due to the incomplete Li removal from Sn after the first cycle. Although the largest capacity loss in SnO electrode is a result from the lithia formation during the first discharge, additional capacity loss arises from the residual Li in metallic Sn owing to the aggregation of Sn upon repeated cycling. Contrary to the previous studies, Li22Sn5 phase is not observed in the discharge product in Sn and SnO electrodes. The LiSn alloy electrode shows almost 100% cycling efficiency at the first cycle due to the pre-existing Li. [Copyright &y& Elsevier]

Abstract: The electrochemical lithiation–delithiation reaction was examined for LiMnPO4 in which different cations were substituted for part of Mn. The X-ray diffraction analysis indicated that LiMnPO4 is tolerant, to some extent, to substitution of Mg2+, Ca2+ and Zr4+. The substitution of Mg2+ and/or Zr4+ led to an increased reversible capacity and a reduced polarization, whereas Ca2+ substitution had a detrimental effect on the electrochemical properties. The potential transient analysis showed that LiMn0.88Mg0.1Zr0.02PO4 has higher lithium diffusivities than pure LiMnPO4, indicating facilitated diffusion kinetics in the substituted material. Upon the first charge–discharge cycle, LiMn0.88Mg0.1Zr0.02PO4 suffered less irreversible capacity loss when compared with LiMnPO4, and smaller amounts of electrolyte salt-based species were detected on the electrode surface of LiMn0.88Mg0.1Zr0.02PO4. [Copyright &y& Elsevier]

Highlights from the article: Cover Feature: Rational Design of a Composite Electrode to Realize a High-Performance All-Solid-State Battery (ChemSusChem 12/2019) Keywords: electrode fabrication; ionic liquid; Li ion; solid-state batteries; solid electrolyte Li ion, ionic liquid, solid electrolyte, electrode fabrication, solid-state batteries.

Rechargeable metal-air batteries are considered a promising energy storage solution owing to their high theoretical energy density. The major obstacles to realising this technology include the slow kinetics of oxygen reduction and evolution on the cathode (air electrode) upon battery discharging and charging, respectively. Here, we report non-precious metal oxide catalysts based on spinel-type manganese-cobalt oxide nanofibres fabricated by an electrospinning technique. The spinel oxide nanofibres exhibit high catalytic activity towards both oxygen reduction and evolution in an alkaline electrolyte. When incorporated as cathode catalysts in Zn-air batteries, the fibrous spinel oxides considerably reduce the discharge-charge voltage gaps (improve the round-trip efficiency) in comparison to the catalyst-free cathode. Moreover, the nanofibre catalysts remain stable over the course of repeated discharge-charge cycling; however, carbon corrosion in the catalyst/carbon composite cathode degrades the cycling performance of the batteries. [ABSTRACT FROM AUTHOR]

Abstract: We report on the capacity fading mechanism of Li-ion batteries consisting of a graphite negative electrode and an olivine LiFePO4 positive electrode during long-term cycling. Laminated pouch type 1.5 Ah full cells are cycled 1000–3000 times at a rate of 4C and the full cells exhibit capacity losses of 10–15%. Half-cell study after full cell disassembly, using degraded electrodes, shows that considerable capacity loss occurs for the negative electrode even at low rates, but the total rate performance of the negative electrode is relatively better than that of the positive electrode. The initial capacity of the positive electrode is largely recovered under low rate conditions (0.1–0.5C), whereas a decline in the reversibility is observed at higher rates (1–5C). Loss of the active lithium source from the system is proposed as a primary source of capacity fading for the full cells. This loss is attributed to a change of the solid electrolyte interface during cycling as well as physical deterioration of the negative electrode due to the intrinsic volume change of the graphite electrode. On the other hand, the increased electrode resistance in the positive electrode is suggested to be the root cause of power fading. [Copyright &y& Elsevier]

Abstract: The electrochemistry of a non-aqueous redox flow battery employing nickel and iron bipyridine in tetraethylammonium tetrafluoroborate and propylene carbonate has been investigated. Ni(0)/Ni(II) and Fe(II)/Fe(III) redox couples showed reversible reactions for negative and positive electrodes, respectively. Various metal electrodes (Pt, Ir, Ni, Cu, Mo, W, Nb, Co, and Ti) were evaluated for those couples using cyclic voltammetry. Based on the analysis of the cyclic voltammograms, the reactivity and kinetics for the electrochemical reaction of metal complexes were found to strongly depend on the type of metal electrodes. Among non-precious metals, Cu and Mo showed relatively better electrocatalytic activities as negative electrodes for the Ni(0)/Ni(II) redox couple and Ni was the best material as a positive electrode for the Fe(II)/Fe(III) redox couple in terms of electrochemical reactivity and reaction kinetics. [Copyright &y& Elsevier]

Abstract: 1,3,5-trihydroxybenzene (THB) is examined as a film-forming additive for over-lithiated layered oxide positive electrode. The surface film generated from the carbonate-based electrolyte (THB-free) is thermally/electrochemically unstable to be dissolved or decomposed during elevated-temperature cycling. Due to this instability, electric charges are consumed in every cycle for electrolyte decomposition to give a low coulombic efficiency. In contrast, the protective film that is generated by oxidative decomposition of the additive (THB) prior to the carbonate electrolyte is robust enough to remain intact. As a result, a full-cell comprising graphite/over-lithiated layered oxide gives a higher coulombic efficiency and longer life cycle. [Copyright &y& Elsevier]